The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Light-Emitting Diodes (LEDs) are semiconductor devices that convert electric current to light. A color of the light emitted by an LED is determined by an energy band gap of the semiconductor. The color may range from infrared (e.g., 940 nm wavelength) to ultraviolet (e.g. 210 nm wavelength).
LEDs emitting different colors of light may have different operating voltages. Furthermore, the relationship between current and light output power varies between different types and colors of LEDs, and may be nonlinear.
LEDs with energy band gaps that produce infrared, red, orange, yellow, green, blue, violet, and ultraviolet light have been developed. In addition, LEDs have been developed that illuminate a phosphor to create additional colors of light.
A plurality of different colors of light can be combined to produce other colors of light, including a white light. The “whiteness” of the white light produced is measured by correlating the produced white light to light emitted by a black body radiator of a given temperature to determine a Correlated Color Temperature (CCT). For example, light having a CCT of 2700° Kelvin (K) is considered “warm white,” and sunlight has a CCT of 4500° K.
The amount of light emitted by an LED may be controlled by varying the magnitude of a current flowing through the LED. Reducing the current through an LED dims the LED, that is, lowers the amount of light emitted by the LED. An LED may also be dimmed by rapidly turning the LED on and off while varying a ratio of an on time to an off time of the LED, that is, by varying the duty cycle of the LED.
When light from a plurality of LEDs having different colors are combined, the resulting color of the light produced may vary as the plurality of LEDs are dimmed. Furthermore, manufacturing tolerances of LEDs and changes over time in LEDs may also cause the resulting color to vary.